Definition
A cold-working process in which the end of a metal tube is spread outward into a conical shape so it can seat against a matching fitting and form a leak-tight seal when tightened with a sleeve and nut. In aviation use, the flare is typically formed at either a 37-degree angle (AN/MS standard) or a 45-degree angle (automotive standard), and the two are not interchangeable.
Plain English
Flaring is when you take the end of a metal tube and spread it outward like a small funnel so it can press tightly against a fitting and not leak. The cone-shaped end gets squeezed between two parts of the fitting to make the seal.
Context Anchor
Seen in aircraft maintenance when making or repairing metal fuel, oil, hydraulic, or brake lines.
Derivation
Flare' comes from the idea of something spreading outward, like a flame spreading from a torch or the bell shape of a trumpet. The tube end literally flares outward from a straight pipe into a cone.
Why Pilots Care
Proper flaring prevents leaks in critical fluid systems that could lead to engine failure or loss of control.
Intuition Check
Tube flaring is not just bending or forcing a tube open. It is making a precise shaped end that can seal against the correct connector.
Example Sentence 1
After cutting the new hydraulic line to length, the technician deburred the end and used a flaring tool to form a 37-degree flare before installing the sleeve and nut.
Example Sentence 2
After tube flaring, the mechanic inspected the cone angle to ensure it would seal correctly under pressure.